1. Field of the Invention
This invention relates to a hydrostatic drive system having a load-sensing pump with an adjustable discharge volume and at least one consumer connected to the pump. The discharge volume of the pump can be set by means of a discharge volume control device that sets the delivery pressure available in a delivery line of the pump so that it is higher by a pilot control pressure difference than the load pressure of the consumer.
2. Technical Considerations
Load-sensing drive systems are used in mobile work machines, for example in construction equipment in the form of excavators, as well as in industrial trucks. A drive system is described in DE 196 15 593 A1. In that case, the discharge volume control device of the pump has a load-sensing control valve. The load-sensing control valve is actuated by the highest load pressure of the consumers being actuated and by a spring (the bias of which is equal to a pilot control pressure difference) toward an increase of the delivery flow of the pump, and by the delivery pressure delivered by the pump toward a reduction of the delivery output. The pump thereby delivers an output having a delivery pressure that is higher by the pilot control pressure difference exerted by the spring than the highest load pressure of the actuated consumers. With a drive system of this type, the consumers can be operated independently of the load at a speed of movement that is specified by the opening width of a control valve.
In the drive system described in DE 196 15 593 A1, the discharge volume control device of the pump is hydraulically controlled by the load-sensing control valve. For the measurement and transmission of the highest load pressure of the consumers to the load-sensing flow control valve, load pressure signal lines are necessary. This entails a great deal of construction effort and the signal lines are prone to leaks, which result in inaccuracies of the output flow control of the pump. The load pressure signal lines are also subject to the effects of temperature, which lead to variations of the load pressure and, thus, to inaccuracies in the control of the output flow of the pump. On mobile work machines, in particular on excavators, the load pressure signal lines can be of a significant length. As a result of which, the transmission of the load pressure of the consumer to the load-sensing flow control valve takes a long time and, thus, the movement of the consumer has a long reaction time as a result of the delayed regulation of the output flow of the pump.
Therefore, it is an object of this invention to provide a hydrostatic drive system of the general type described above but that makes possible an improved reaction of the consumers with little construction effort.